Clean up the default gamma settings.

This makes it a compile error to specify both SK_GAMMA_EXPONENT
and SK_GAMMA_SRGB. It also ensures that SK_GAMMA_EXPONENT will
be set consistently.

R=djsollen@google.com, reed@google.com

Review URL: https://codereview.chromium.org/233003003

git-svn-id: http://skia.googlecode.com/svn/trunk@14143 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed